Sounds fine. Now, I've never kept livebearers, but from what I gather, Mollies prefer higher pH, and warmer temp (80-82F). I would suggest raising the tank to 80 over next days, or see how they do w/ the up at 78 first. You're salting the tank, which is the other reccomendation I came across.
On shimmies, what I find is temp drop, possibly parasites, something amiss in the water (lack of electrolytes, which I think can be covered by the salt, not sure).
For now, I think I'd look at the water....but if the FMG worked, and you go w/ that, careful on increasing temp...see that they have enough oxygen. I also saw mention of a 'Shimmy Block'....apparently copper-based. Not sure of the effects of copper, but perhaps worth looking into.
Do they get veggies in their diet?
Never heard of 'shimmy fungus'?
